Faster DC solenoid release time

[jstein]

I am looking for the fastest way to release a 12volt soleniod after it is de-energized. Every ms counts. Reducing the voltage after energizing? How? What else? Thanks!

 

[MikeHalloran]

It's important to understand that the entire drive circuit affects the performance of a solenoid, so much so that any timing specifications given are meaningless without the details of the drive circuit used for testing.

To get best results, you need a real serious sparky type.

In the meantime, a back- biased diode across the drive transistor or relay contacts will suck the stored energy out of the solenoid pretty quickly. You will smoke a few diodes until you find one massive enough to survive. The diode becomes a short circuit for the voltage generated by the collapsing field. It's not an application for a small signal diode.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[sreid]

Assuming the solenoid is being driven by a transistor;

A "Catch Diode" across the coil is the slowest way to dump the current. A resistor in series with the diode will dump the current faster ( the time constant is L/R ). The voltage on the transistor will jump to the solenoid current times R.

Even faster will be a zener diode in series with the diode. The transistor will see a voltage jump equal to the zener voltage. Use a surge suppressor zener like a 1.5KExxx where xxx is voltage.

The fastest; most power FETs are energy rated for breakdown as a power zener diode. If the 1/2 LI^2 in the solenoid is lower than the breakdown power rating of the FET you can let the FET zener the solenoid

 

[itsmoked]

The fastest method is energy control. The waveform sent to the solenoid is specifically profiled. For instance a high initial pulse is used to get things moving but the current is quickly reduced before the solenoid is even fully retracted. Then a very low holding current is maintained before de-energizing.

 

[Marke]

Hello jstein

Any impedance across the solenoid coil when you open it, will extend the release time.
The problem is that when the driving circuitry releases the solenoid, there will be a high voltage generated. This can cause failure of the driving circuit. In order to protect the driving circuit, reverse diodes across the coil are common. This restricts the voltage to 0.6 Volt above the supply voltage. Adding a resistor in series with the diode will increase the switch OFF voltage across the switching device and speed up the switch OFF time.
My suggestion is to increase the voltage rating of the switching device as high as possible - hundreds of volts rather than tens of volts, and use overvoltage protection that only begins to conduct current close to the voltage rating of the device. Try to eliminate as much capacitance as possible and be aware of the affect of the millar capacitance of the output device. If you use a bipolar transistor, make the resistance between the base and emitter as low as possible. If you use a MOSFET, use a low value of gate source resistor. If you can apply a negative bias during switch OFF, the device will switch quicker and the solenoid will release quicker.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[Barry1961]

Is there any way to reduce the number of turns on the coil? You may be able to trade power consumption for speed with less turns and higher current. Inductors are great for taking short spikes of high current.

You may also have more magnetic force than you need.

Barry1961

 

[OperaHouse]

If you really want to operate a solenoid fast, don't have all that energy in the solenoid to start. In many cases you can reduce the coil current by 75% easily after it has pulled in. I've built solenoid drivers for clunky glue valves and driven them as fast as 2ms on and 2ms off. There are a number of solenoid driver chips that easily do this with PWM. I've found the limiting factor is the mechanics, not the electronics. All that noise supression slows things down. Design the electronics so it can tolerate the spikes.

 

[nbucska]

Please read the FAQ.
Can U tell us more about your application?

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[jstein]

This soleniod is for stopping fluid flow and is located in ambient air.It draws about 10 amps at 12volts. It is controled by hand with a simple momentary switch. Energizing time is not an issue. There are no electronics involved. Thanks for your thoughts!

 

[sreid]

In that case, putting a small capacitor across the relay contacts will speed up the current collapse. This is just like the "Condenser" across ignition points (if anyone remembers those).

 

[Lakey]

Are you able to increase the srength of the return spring - if there is one used.

Regards,

 

[nbucska]

Since the human can't respond in 2msec, the problem must be not the timing of the turn-off but the ramping off the
flow i.e. the slope.

Could you use a voice-coil type ectuator ( electro- AND
permanent magnets ) or a faster valve?


<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[buzzp]

sreid is correct concerning coil suppression devices and release times. Follow-up on this and pursue the idea of PWM to reduce the stored energy and decrease the release time. Alot can be gained in release times by careful attention to the devices across the coil. See Potter & Bromfield (tyco electronics) app note 13C3311. It charts release times very well vs. coil suppression methods. They also have some other relavent useful info.

 

[OperaHouse]

I think you need to look at the valve design. I could design you some really fast electronics and it wouldn't solve your problem. In many valves the solenoid only operates a pilot valve that operates a bellows of the real valve. The time delay you might be seeing is the ability of the valve to dunp fluid out of the bellows.

 

[frankeng9]

Hi jstein,

There is one additional item that you might want to consider regarding the “release time” of your solenoid. All of the previous posts regarding the use of a diode across the coil winding to quickly suppress the back EMF voltage (and drop-out time) in the coil during turn-off are right on target. A diode AND series resistor across the coil will improve the drop-out time of the coil. However, an additional item critical in solenoid response time is the magnetic circuit itself. I have seen several poorly designed solenoid’s (commercial and OEM) where the coil and internal magnetic circuit were not properly sized. As a result, the flux produced within the magnetic circuit eventually drove all the solenoid’s internal parts into magnetic saturation. When the current was shut off, the field in the coil quickly collapsed, however the moving part of the solenoid (the plunger) was now a small permanent magnet, and delayed the “release” of the moving parts by as much as 20 times as that as for a non-saturated circuit. One suggestion as a test to see if your solenoid has succumbed to this phenomenon, would be to place a small non-magnetic shim (say 0.015 inches of brass) in between the moving and stationary parts of the solenoid (if you can get at it without destroying the whole thing). Increasing the final air-gap in this manner will have a positive effect on the release time of the solenoid, and may help you to diagnose your problem. Hope this helps – good luck.

 

[Lakey]

A question for Frankeng9 if I may: -

Frank, assuming DC, how do you test the magnetic frame to ensure that it is not in saturation?

Are you saying that the frame is certainly saturated If the moving core sticks to the stop when the coil is de-energised?

Thanks & regards,